Whither ARM?

Although many questions about Windows 8 were answered at Build, there is still some confusion surrounding Windows 8 running on ARM-based devices.

Windows support for processors based on the ARM architecture, originally announced in Jan. 2011, has attracted considerable attention because the most popular tablets and smartphones today use that architecture. Some demonstrations at Build were done on ARM systems, and Stephen Sinofsky, president of the Windows and Windows Live division, stated that Metro applications will run on both x86 and ARM-based Windows 8 devices, regardless of the development language used for implementation.

Nevertheless, the majority of the Build demos and the Windows 8 preview code provided to developers targets x86 and x64 processors, not ARM. In general, Windows 8 on x86 and x64 hardware should have good backward compatibility with applications written for Windows 7. “If it runs on a Windows 7 PC, it’ll run on Windows 8,” Sinofsky said.

However, Microsoft will not provide processor emulation in Windows 8, meaning that existing Windows application binaries created for x86 and x64 computers cannot run on ARM-based devices. Furthermore, the company might not even support running standard, non-Metro Windows applications on ARM processors. Microsoft demonstrated such an application (a port of Word) in Taipei at the Computex hardware conference in Jan. 2011, but it may have been a proof of concept rather than a product Microsoft plans to release. The company did not present ARM ports of Office or any other existing Windows applications at Build, demonstrating only sample Metro applications. Furthermore, Sinofsky questioned the wisdom of running existing Windows applications on ARM mobile devices, observing, for example, “Those applications aren’t written to be really great in the face of limited battery constraints, which is a value proposition of the Metro-style apps.”